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The need for evidence-based strategies and tools for onchocerciasis elimination in Africa.

ABSTRACT: In a recent article we discussed the feasibility of onchocerciasis elimination in Africa by 2025. We expressed concern that elimination may be impeded by failure to build on the lessons learned in the African onchocerciasis control programmes and the introduction of strategies and tools from the Americas. Richards et al. and Cupp et al. wrote to refute our concern and described recent achievements with stopping treatment in some areas.In this response, we discuss their arguments which did not convince us. We point out several scientific flaws in the American conceptual framework of elimination which has led to longer periods of treatment than necessary, and in the use of an arbitrary threshold for stopping treatment. We show that recent achievements fall significantly short of what would be needed to achieve onchocerciasis elimination by 2025.We conclude our response by advocating for a more objective and inclusive debate on strategies and tools for onchocerciasis elimination.

SUBMITTER: Dadzie Y

PROVIDER: S-EPMC6628483 | biostudies-literature | 2019 Jul

REPOSITORIES: biostudies-literature

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The need for evidence-based strategies and tools for onchocerciasis elimination in Africa.

Dadzie Yankum Y Amazigo Uche V UV Boatin Boakye A BA Sékétéli Azodoga A

Infectious diseases of poverty 20190715 1

In a recent article we discussed the feasibility of onchocerciasis elimination in Africa by 2025. We expressed concern that elimination may be impeded by failure to build on the lessons learned in the African onchocerciasis control programmes and the introduction of strategies and tools from the Americas. Richards et al. and Cupp et al. wrote to refute our concern and described recent achievements with stopping treatment in some areas.In this response, we discuss their arguments which did not co ...[more]

PMID: 31303174

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Project description:BackgroundMass treatment with ivermectin is a proven strategy for controlling onchocerciasis as a public health problem, but it is not known if it can also interrupt transmission and eliminate the parasite in endemic foci in Africa where vectors are highly efficient. A longitudinal study was undertaken in three hyperendemic foci in Mali and Senegal with 15 to 17 years of annual or six-monthly ivermectin treatment in order to assess residual levels of infection and transmission and test whether ivermectin treatment could be safely stopped in the study areas.Methodology/principal findingsSkin snip surveys were undertaken in 126 villages, and 17,801 people were examined. The prevalence of microfilaridermia was <1% in all three foci. A total of 157,500 blackflies were collected and analyzed for the presence of Onchocerca volvulus larvae using a specific DNA probe, and vector infectivity rates were all below 0.5 infective flies per 1,000 flies. Except for a subsection of one focus, all infection and transmission indicators were below postulated thresholds for elimination. Treatment was therefore stopped in test areas of 5 to 8 villages in each focus. Evaluations 16 to 22 months after the last treatment in the test areas involved examination of 2,283 people using the skin snip method and a DEC patch test, and analysis of 123,000 black flies. No infected persons and no infected blackflies were detected in the test areas, and vector infectivity rates in other catching points were <0.2 infective flies per 1,000.Conclusion/significanceThis study has provided the first empirical evidence that elimination of onchocerciasis with ivermectin treatment is feasible in some endemic foci in Africa. Although further studies are needed to determine to what extent these findings can be extrapolated to other endemic areas in Africa, the principle of elimination has been established. The African Programme for Onchocerciasis Control has adopted an additional objective to assess progress towards elimination endpoints in all onchocerciasis control projects and to guide countries on cessation of treatment where feasible.

Project description:Recent evidence suggests that, in some foci, elimination of onchocerciasis from Africa may be feasible with mass drug administration (MDA) of ivermectin. To achieve continental elimination of transmission, mapping surveys will need to be conducted across all implementation units (IUs) for which endemicity status is currently unknown. Using boosted regression tree models with optimised hyperparameter selection, we estimated environmental suitability for onchocerciasis at the 5 × 5-km resolution across Africa. In order to classify IUs that include locations that are environmentally suitable, we used receiver operating characteristic (ROC) analysis to identify an optimal threshold for suitability concordant with locations where onchocerciasis has been previously detected. This threshold value was then used to classify IUs (more suitable or less suitable) based on the location within the IU with the largest mean prediction. Mean estimates of environmental suitability suggest large areas across West and Central Africa, as well as focal areas of East Africa, are suitable for onchocerciasis transmission, consistent with the presence of current control and elimination of transmission efforts. The ROC analysis identified a mean environmental suitability index of 0·71 as a threshold to classify based on the location with the largest mean prediction within the IU. Of the IUs considered for mapping surveys, 50·2% exceed this threshold for suitability in at least one 5 × 5-km location. The formidable scale of data collection required to map onchocerciasis endemicity across the African continent presents an opportunity to use spatial data to identify areas likely to be suitable for onchocerciasis transmission. National onchocerciasis elimination programmes may wish to consider prioritising these IUs for mapping surveys as human resources, laboratory capacity, and programmatic schedules may constrain survey implementation, and possibly delaying MDA initiation in areas that would ultimately qualify.

Project description:BackgroundOnchocerciasis is found predominantly in Africa where large scale vector control started in 1974. Registration and donation of ivermectin by Merck & Co in 1987 enabled mass treatment with ivermectin in all endemic countries in Africa and the Americas. Although elimination of onchocerciasis with ivermectin was considered feasible only in the Americas, recently it has been shown possible in Africa too, necessitating fundamental changes in technical and operational approaches and procedures.Main bodyThe American programme(OEPA) operating in onchocerciasis epidemiological settings similar to the mild end of the complex epidemiology of onchocerciasis in Africa, has succeeded in eliminating onchocerciasis from 4 of its 6 endemic countries. This was achieved through biannual mass treatment with ivermectin of 85% of the eligible population, and monitoring and evaluation using serological tests in children and entomological tests. The first African programme(OCP) had a head start of nearly two decades. It employed vector control and accumulated lots of knowledge on the dynamics of onchocerciasis elimination over a wide range of epidemiological settings in the vast expanse of its core area. OCP made extensive use of modelling and operationalised elimination indicators for entomological evaluation and epidemiological evaluation using skin snip procedures. The successor African programme(APOC) employed mainly ivermectin treatment. Initially its objective was to control onchocerciasis as a public health problem but that objective was later expanded to include the elimination of onchocerciasis where feasible. Building on the experience with onchocerciasis elimination of the OCP, APOC has leveraged OCP's vast modelling experience and has developed operational procedures and indicators for evaluating progress towards elimination and stopping ivermectin mass treatment of onchocerciasis in the complex African setting.ConclusionsFollowing the closure of APOC in 2015, implementation of onchocerciasis elimination in Africa appears to overlook all the experience that has been accumulated by the African programmes. It is employing predominantly American processes that were developed in a dissimilar setting from the complex African onchocerciasis setting. This is impeding progress towards decisions to stop intervention in many areas that have reached the elimination point. This article summarizes lessons learned in Africa and their importance for achieving elimination in Africa by 2025.

Project description:BackgroundOnchocerciasis (river blindness) is a parasitic disease transmitted by blackflies. Symptoms include severe itching, skin lesions, and vision impairment including blindness. More than 99% of all cases are concentrated in sub-Saharan Africa. Fortunately, vector control and community-directed treatment with ivermectin have significantly decreased morbidity, and the treatment goal is shifting from control to elimination in Africa.MethodsWe estimated financial resources and societal opportunity costs associated with scaling up community-directed treatment with ivermectin and implementing surveillance and response systems in endemic African regions for alternative treatment goals--control, elimination, and eradication. We used a micro-costing approach that allows adjustment for time-variant resource utilization and for the heterogeneity in the demographic, epidemiological, and political situation.ResultsThe elimination and eradication scenarios, which include scaling up treatments to hypo-endemic and operationally challenging areas at the latest by 2021 and implementing intensive surveillance, would allow savings of $1.5 billion and $1.6 billion over 2013-2045 as compared to the control scenario. Although the elimination and eradication scenarios would require higher surveillance costs ($215 million and $242 million) than the control scenario ($47 million), intensive surveillance would enable treatments to be safely stopped earlier, thereby saving unnecessary costs for prolonged treatments as in the control scenario lacking such surveillance and response systems.ConclusionsThe elimination and eradication of onchocerciasis are predicted to allow substantial cost-savings in the long run. To realize cost-savings, policymakers should keep empowering community volunteers, and pharmaceutical companies would need to continue drug donation. To sustain high surveillance costs required for elimination and eradication, endemic countries would need to enhance their domestic funding capacity. Societal and political will would be critical to sustaining all of these efforts in the long term.

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The need for evidence-based strategies and tools for onchocerciasis elimination in Africa.

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The need for evidence-based strategies and tools for onchocerciasis elimination in Africa.

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